Tuscon to Tucumcari…

“Tehachapi to Tonapah..”

Tell me again why Little Feat isn’t in the Rock ‘N Roll Hall of Fame while ABBA is?

Been talking about how sometimes what looks like the “right” pump can turn out to be the “wrong” pump (here and here to review). And if you’re still willin’, lets wrap this up.

Our problem is one of pump curves.  The old circulator in this job was a high-flow, low-head flat curve pump.  As zone valves closed there was no real change in the pressure differential created by the circulator.  Result – no noise.

The new system had new 3-speed circulators (first the Taco 0015, then the Grundfos 15-58).  Both are lower-flow, higher-head steep curve pumps, and as zone valves closed there was a big increase in pressure differential.  The system curves backed up the pump curves and the zone valves had to close against greater and greater pressure differentials.

Zone valves don’t like that. Hence the banging. Soooo…..

How do we make the banging stop?

There are three possible solutions, ranging from the simple to the silly.  Let’s start with silly.

Option 1: Install a pressure differential bypass valve

Why is this silly? Because it’s the most labor-intensive (and as a result, most costly) and least effective solution of the three. Installing a pressure differential bypass valve involves isolating and/or draining the system, altering the boiler piping to accommodate the valve, piping the valve correctly and setting the valve up properly (not a “gimme” by any means).

That’s a lot of time, material and effort for what amounts to a “band-aid.”

And that’s all a pressure differential bypass valve is, really – a band-aid.  It masks the fact that the wrong pump was installed in the first place.  The bypass valve does have its place, but the instances where one is necessary are few and far between.

The bypass valve will stop the banging in this job by turning the steep-curve pumps into a flat-curve pump.  That’ll most likely solve the problem (provided it’s set up properly!), but why do that when you can…

Option 2: Install a flat-curve pump.

This is the solution that actually solved the problem – although the wholesaler took some convincing.  He was going to have his contractor install a bypass valve (“that’s how they do it in Europe!)” and figured he’d have to eat the cost.  Told him it’d be easier, less costly and more effective to simply swap out the 3-speed step curve pump for the right pump – a flat-curve Taco 007.

“That can’t be it – the 007 is such old technology.  It’s been around forever!”

It sure has, but the laws of physics have been around even longer.  Steep curve pumps make zone valves go bang – doesn’t matter who makes ‘em, how fancy they are or their continent of origin.  Just think square pegs and round holes – they don’t fit the application.  If you have a round hole, use a round peg. It’s easier that way.

The contractor installed the “old-school” Taco 007 and, saints preserve us, the banging went away.

Oh, the third option?  We’ll deal with that next time.

Because time, after all, love a hero…


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